1. Field of the Invention
The present invention relates to a polyester fiber containing silica-based inorganic particles and a method for making a polyester composition. The polyester fiber of the present invention exhibits high hygroscopicity and is suitable for comfortable materials, such as underwear, sportswear, and lining, in the form of woven and knitted fabrics. Herein, the term “comfortable material” means a material requires comfortableness when the material is used in high-temperature and high-humidity environments.
2. Description of the Related Art
Polyesters, such as polyethylene terephthalate (hereinafter, referred to as PET), exhibit excellent physical and chemical properties, and have been widely used as fibers, films, and molded articles. However, PET is hydrophobic and less hygroscopic. When being used in clothes, PET causes sweaty in highly humid environments and generates static electricity. Thus, PET is not a comfortable material as clothes. When it is used as resins and films, electrostatic charge due to low hygroscopicity would cause problems.
In order to solve these problems, methods for copolymerizing or adding hygroscopic compounds to polyesters have been proposed. For example, copolymerization with a diol having oxyalkylene glycol side chains and copolymerization with a dicarboxylic acid containing metal sulfonate are disclosed. These methods for copolymerizing the hygroscopic components, however, cause decreases in mechanical strength and weather resistance.
In addition to the above modification methods of polyesters, methods for bonding hygroscopic compounds to polyester fibers have been proposed. For example, acrylic acid or methacrylic acid is graft-polymerized to polyester fibers and these carboxyl groups are allowed to react with alkali metals to improve hygroscopicity. Hygroscopic compounds bonded to the fiber surface cause generation of slime, a decrease in strength over time, and a decrease in weather resistance.
In order to solve these problems, core-sheath bicomponent fibers have been proposed in which cores of highly hygroscopic resins are covered with polyester sheaths. In the core-sheath bicomponent fibers, however, the core hygroscopic resins are swollen with water during hot-water treatments, such as scouring and dyeing, resulting in cracking on the fiber surface (sheath cracking), effluence of the hygroscopic resins to the exterior, and a decrease in textile quality due to insufficient color fastness.
In order to solve these problems, various methods using hygroscopic inorganic particles instead of the hygroscopic organic compounds and resins have been proposed. When the hygroscopic inorganic particles are contained in general polyesters, active groups of the hygroscopic inorganic particles are embedded in the polymers. Thus, the polyesters do not exhibit sufficient hygroscopicity. Japanese Unexamined Patent Application Publication No. 8-113827 discloses a fiber in which a polyether ester is used as a base polymer instead of polyester and silica gel microparticles are compounded. In this method, some hygroscopicity is imparted to the fiber due to slight hygroscopicity of the polyether ester. However, the polyether ester base polymer has inferior mechanical strength compared with polyesters.